- Add gapless and preroll support. This requires some libavformat integration but the lossless codecs must at least have some sort of gapless support. Support for the iTunSMPB tag is a must.
- Optimize the SBR windowing. The actual transform should be fairly optimal. See the implementation notes from my first blog post.
- Optimize the parametric stereo filterbank. There is a lot of redundant math in there.
- Add fixed point support.
- Consider a more conservative approach to SBR and PS detection. (If there is no signaling and the sample rate is less than or equal to 24 kHz assume SBR. If SBR is used and the stream is mono assume PS).
Seeing as I resigned from being the FFmpeg AAC maintainer, here is my remaining decoder todo list for those interested in hacking on the decoder: